With empty land at a premium in densely populated urban areas, builders have long reached into the sky to maximize the amount of residential or commercial space they can develop.

Now a team of Spanish architects has proposed doing the same thing with green space, creating an eye-catching design for a multipurpose vertical garden that would be at home in a city center or a park.The Guggenheim-esque "Spiral Garden," GOOD writes, incorporates "a public vertical garden, a botanical-garden-like place where people can take a stroll, 170 parking spots for bikes, and a composting center where people can drop off their scraps."

The design team of Benet Dalmau, Saida Dalmau, Anna Julibert, and Carmen Vilar won a Designboom IIDA Award for the concept, which they described as a "public sustainable place like a green heart" that helps make the environment an integral part of everyday life:

A light, spiral structure protected by a transparent and suggestive mesh, the project encourages the city to create sustainable exchange spaces in different ways. This spiral contains an ascending garden where native vegetation can coexist with urban orchards, shared and planted for the neighbours for easy maintenance and serving also as a green outdoor walk. 'Spiral garden system' increases social interaction between people, provides a place for exchanging natural products, and becomes a way for local residents to get involved with their neighbourhood.

The Spaniards aren't the only one thinking vertically when it comes to gardens. A separate Designboom piece on the urban-agriculture think tank Growingcity features other innovative ways to reduce major cities' importation of an average of 6,000 tons of food each day. These creative minds envision incorporating greenhouse-style gardens of various sizes into housing developments, lampposts, even underneath workers' desks.

Growth in Garden SharingUntil ideas like these become reality, urban dwellers can find places to garden the same way they find dates, roommates, jobs, and apartments: through social networking. A bumper crop of "garden sharing" sharing websites -- including We Patch, Yardsharing, and Shared Earth in the United States, and Landshare in Britain -- is connecting people who want to grow food with underutilized space, potentially turning cities into real-life Farmvilles.